Field of the Invention
The invention concerns a method for controlling a magnetic resonance apparatus, wherein a sequence of synchronized, i.e. coordinated, control commands is transmitted to different system components of the magnetic resonance apparatus. The invention also concerns a controller for carrying out a method of this type, and to a magnetic resonance apparatus having a controller of this type.
Description of the Prior Art
In a magnetic resonance apparatus, also called a magnetic resonance tomography system, the body to be examined is conventionally exposed, with the use of a basic field magnet, to a relatively high basic magnetic field, for example of 1.5 tesla, 3 tesla or 7 tesla, in order to create magnetic resonance scans. In addition, a magnetic field gradient is applied with the use of a gradient system. Radio-frequency excitation signals (RF signals) are then emitted by a radio-frequency transmitting system by suitable antenna devices, and this is intended to tilt the nuclear spins of specific atoms resonantly excited by this radio-frequency field, by a defined flip angle with respect to the magnetic field lines of the basic magnetic field. When the nuclear spins are relaxed, radio-frequency signals, known as magnetic resonance signals, are emitted, which are received by a radio-frequency receiving system by suitable receiving antennae, and then processed further. Finally, the desired image data can be reconstructed from the raw data acquired in this way.
For a specific scan, a specific a pulse sequence should be emitted, and this includes a sequence of radio-frequency pulses, in particular excitation pulses and refocusing pulses, and appropriate gradient pulses that are to be emitted in a coordinated manner in various directions. Readout windows for the radio-frequency receiving system are set at a time appropriate therewith, during which the induced magnetic resonance signals are detected. Particularly crucial to the imaging is the timing within the sequence, i.e. the intervals at which pulses follow each other.
Particularly exact coordination or synchronization of the application of gradient fields, radio-frequency transmitting fields and receive events, i.e. activation of the respective receiving devices of the radio-frequency receiving system, is necessary. The requirements of the coordination accuracy are in the range of 1 ns to 100 μs.
For this purpose, the individual system components of the magnetic resonance system, such as the gradient system, radio-frequency transmitting system and radio-frequency receiving system, must be addressed equally exactly. Each of these system components (which can also be regarded as subsystems of the magnetic resonance system) obviously has further subcomponents, such as the gradient amplifiers (conventionally called GPAs=Gradient Power Amplifiers) of the gradient system and the radio-frequency transmission amplifiers (conventionally called RFPAs=Radio Frequency Power Amplifiers) of the radio-frequency transmission system or generally different DACs (Digital Analog Converters) and/or ADCs (Analog Digital Converters). To control the amplifiers, for example the digital signals generated by the controller of the magnetic resonance system are converted into analog signals by DACs and processed further. Conversely, when the magnetic resonance signals, which arrive back at the receiving antennae from the excited spins, are received it is necessary to convert the analog signals into digital signals by the use of ADCs. The individual amplifiers, DACs and ADCs or further subcomponents of the various components or subsystems of the magnetic resonance system are often situated at physically separate locations, for example on different boards or even in different switching cabinets or rooms in the practice or hospital. It is also possible, particularly in the case of a high number of received signals, for a number of components to exist for each component or device type (such as, for example, gradient DACs, radio-frequency transmission DACs, radio-frequency receive ADCs), which can likewise again be spatially distributed.
In addition, there is also a large number of further optional components or subsystems, such as shim systems, camera systems, monitoring systems, table-positioning sensors and table-positioning systems, patient monitoring devices, etc., which must also receive their commands in synchronization with the system components mentioned above, and can similarly have further subcomponents.
Synchronization of the system components or subsystems mentioned above and the associated device types within the required accuracy range makes high demands on the controller, and therefore has conventionally required the development of proprietary solutions adapted specifically to the respective magnetic resonance system. There are various annular or star-shaped architectures for the distribution of a clock (clock signal) for the standardized system time (i.e. a standardized absolute interval within the magnetic resonance system) as a synchronization signal. In each case, however, proprietary, specifically adapted protocols and systems are developed for each individual magnetic resonance system, and these distribute the clock and the absolute time information to the distributed system components in such a way that the desired synchronization is attained. These proprietary solutions for each newly developed type of magnetic resonance system lead to high development costs and to additional risks with respect to possible development errors.